Improve WaitForPos errors, don't include Result struct in message (#1…

…5962)

Signed-off-by: Rafer Hazen <[email protected]>

go/vt/vttablet/tabletmanager/vreplication/engine.go

@@ -790,8 +790,10 @@ func (vre *Engine) WaitForPos(ctx context.Context, id int32, pos string) error {
 			}
 		case len(qr.Rows) == 0:
 			return fmt.Errorf("vreplication stream %d not found", id)
-		case len(qr.Rows) > 1 || len(qr.Rows[0]) != 3:
-			return fmt.Errorf("unexpected result: %v", qr)
+		case len(qr.Rows) > 1:
+			return fmt.Errorf("vreplication stream received more rows than expected, got %d instead of 1", len(qr.Rows))
+		case len(qr.Rows[0]) != 3:
+			return fmt.Errorf("vreplication stream received an unexpected number of columns, got %d instead of 3", len(qr.Rows[0]))
 		}
 
 		// When err is not nil then we got a retryable error and will loop again.

go/vt/vttablet/tabletmanager/vreplication/engine_test.go

@@ -426,7 +426,8 @@ func TestWaitForPosError(t *testing.T) {
 
 	dbClient.ExpectRequest("select pos, state, message from _vt.vreplication where id=1", &sqltypes.Result{Rows: [][]sqltypes.Value{{}}}, nil)
 	err = vre.WaitForPos(context.Background(), 1, "MariaDB/0-1-1084")
-	want = "unexpected result: &{[] 0 0 [[]]  0 }"
+	want = "vreplication stream received an unexpected number of columns, got 0 instead of 3"
+
 	assert.EqualError(t, err, want, "WaitForPos:")
 
 	dbClient.ExpectRequest("select pos, state, message from _vt.vreplication where id=1", &sqltypes.Result{Rows: [][]sqltypes.Value{{
@@ -435,7 +436,7 @@ func TestWaitForPosError(t *testing.T) {
 		sqltypes.NewVarBinary("MariaDB/0-1-1083"),
 	}}}, nil)
 	err = vre.WaitForPos(context.Background(), 1, "MariaDB/0-1-1084")
-	want = `unexpected result: &{[] 0 0 [[VARBINARY("MariaDB/0-1-1083")] [VARBINARY("MariaDB/0-1-1083")]]  0 }`
+	want = "vreplication stream received more rows than expected, got 2 instead of 1"
 	assert.EqualError(t, err, want, "WaitForPos:")
 }